The present invention relates to an ammonia injection device for injecting ammonia serving as a reducing agent into an exhaust gas duct, for use in exhaust gas denitration systems for removing nitrogen oxides (NOx) from the exhaust gases of gas turbines, boilers, etc. by selective catalytic reduction.
With reference to FIG. 6, exhaust gas systems include an ammonia injection device which is disposed within an exhaust gas duct provided between an NOx-containing exhaust gas source (boiler, heating furnace, gas turbine or the like) and a reactor. The injection device is installed at a specified position where the exhaust gas has an appropriate temperature for supplying to the duct vaporized ammonia gas serving as a reducing agent and supplied from an ammonia production device.
FIG. 7 shows a conventional ammonia injection device, which comprises a pair of vertical header pipes 201 arranged outside respective opposite side walls 101 of an exhaust gas duct 100, a plurality of ammonia injection pipes 202 arranged horizontally within the duct 100 with their opposite ends extending through the duct side walls 101 and each formed with a multiplicity of nozzles (not shown), and a plurality of expansion joints 203 connecting the ends of the injection pipes 202 to the header pipe 201 opposed thereto. The ammonia injection pipes 202 are secured to a plurality of vertical support members 204 arranged inside the duct 100 and thereby prevented from warping or deflecting.
However, the conventional ammonia injection device described has the following problems.
While the ammonia injection pipes 202 have opposite ends extending through the duct side walls 101, the provision of many pipe passing portions in the side walls 101 which portions need to be sealed makes the device complex in construction and requires much labor. Moreover, the multiplicity of expansion joints 203 must be used for absorbing the difference in the amount of thermal expansion between the injection pipes 202 which are exposed to the hot exhaust gas and the header pipes 201 which are positioned externally of the duct 101.
The amount of thermal expansion of the support members 204 increases considerably as the overall size of the device increases, so that the injection pipes 202 secured to these members 204 are likely to be broken by being subjected to pressure by the support members 204 which thermally expand.
The reducing agent, i.e., vaporized ammonia gas, needs to be uniformly injected into the duct 100, whereas when the ammonia injection pipes 202 have an increased length with an increase in the size of the device, there arises the problem that the device fails to effect uniform injection since the amount ammonia injected from the injection nozzle of the pipe 202 away from the header pipe 201 is much smaller than that from the injection nozzle close to the header pipe 201.